1. Field of the Invention
The present invention relates to a semiconductor device in which an oxide semiconductor film is used for a channel formation region, and a method for manufacturing the semiconductor device. For example, the present invention relates to thin film transistors, or electronic devices which are mounted with, as a component, electro-optical devices typified by liquid crystal display panels including a thin film transistor or electronic devices which have light-emitting display devices including an organic light-emitting element.
In this specification, a “semiconductor device” refers to a device which can function by utilizing semiconductor characteristics; an electro-optical device, and an electronic device using a semiconductor circuit and a semiconductor element are all included in semiconductor devices.
2. Description of the Related Art
In recent years, active matrix display devices (such as liquid crystal display devices, light-emitting display devices, or electrophoretic display devices) in which a switching element including a thin film transistor (hereinafter, referred to as a TFT) is provided in each of display pixels arranged in a matrix have been actively developed. In the active matrix display devices, a switching element is provided in each of pixels (or each of dots), and thus, there is such an advantage that the active matrix display devices can be driven at lower voltage than passive matrix display devices in the case where the number of pixels is increased.
In addition, a technique has attracted attention, where a thin film transistor (TFT) or the like in which an oxide semiconductor is used for a channel formation region is manufactured and such a TFT or the like is applied to electronic devices or optical devices. For example, a thin film transistor in which ZnO is used for a channel formation region or a thin film transistor in which an oxide containing indium, gallium, and zinc is used for a channel formation region can be used as such a TFT. Further, Patent Documents 1 and 2 and the like disclose a technique where such a thin film transistor in which an oxide semiconductor is used for a channel formation region is formed over a light-transmitting substrate and used for a switching element or the like of an image display device.